344 



ESSENTIALS OF BOTANY 



hard woods. There are no ducts, and the main bulk of 

 the wood is composed of rather long closed tubes {tracheids) 

 which taper to a point at each end. The rings plainly seen 

 on the cross-section of some kinds of coniferous timber are 



ITiG. 232. Forest of Hard or Yellow Pine (Pinus palustris) on Southern 

 Coastal Plain of the United States. 



(After Frye.) 



due to the difference in diameter of the tracheids formed 

 in early spring and later on (Fig. 233). 



418. Hard Woods. — North America furnishes more spe- 

 cies of trees valuable for hard-wood timber than any other 

 region of similar area with a temperate climate. About 

 eighty kinds are of economic importance, and of these 

 six or eight are oaks, classed for commercial purposes as 

 white and red or black oaks. White oak is stronger than 



